Effect of crude glycerin levels on meat quality and carcass characteristics of crossbred Boer goats

Abstract This study assessed the effects of four levels of crude glycerin (0, 50, 100, and 150 g/kg dry matter (DM) basis) in the diet of Boer crossbred goat kids on the qualitative and quantitative carcass characteristics as well as meat quality. Thirty‐two crossbred, castrated Boer x undefined breed goat kids with an initial average weight of 17.8 ± 2.2 kg between 3 and 4 months of age were distributed across a complete randomized experiment with four treatments and eight replicates. The DM intake linearly decreased (p < .05) as the crude glycerin inclusion level in the diet increased. Crude glycerin levels decreased (linear effect, p < .05) empty body weight, hot dressing percentage, and cold dressing percentage. Conformation and subcutaneous fat thickness were not affected (p > .05) by dietary crude glycerin. Crude glycerin levels decreased (linear effect, p = .03) rib eye area of the Longissimus dorsi muscle, however, did not affect color, cooking loss, and shear force. The crude glycerin can be included up to 50 g/kg DM in the diet of crossbred Boer goats without negatively affecting carcass characteristics and meat quality. It can be recommended as an energy source in finishing diets.


| INTRODUC TI ON
With periodically increasing feed costs, alternative food sources such as crude glycerin (a glycerol-rich source) have become more prominent (Chanjula et al., 2015;Semkiv et al., 2020). The use of crude glycerin avoids its disposal in the environment and contributes to the energetic demands of animals capable of converting this co-product into foods of high nutritional value for humans while also replacing ingredients in animal feed (e.g., corn) whose price varies greatly throughout the year.
The glycerol present in the animal body is usually linked to a lipid source (triglycerides, lipoproteins, or dietary fats). When used in animal feed, however, glycerol is not linked to such sources and is assimilated as an energy source primarily as glucose (Bergman et al., 1968;Carvalho et al., 2015). Only when consumed in excess will glycerol be converted into glycogen in the liver and later transform into fat through lipogenesis. Possibly glycerin does not cause harmful changes to the meat of animals that consume it. Nevertheless, the use of crude glycerin in the diet of ruminants leads to a high | 2313 BEZERRA Et Al. availability of gluconeogenic components because of the conversion of glycerin into propionate, which can be used in fatty acid synthesis (Versemann et al., 2008) and affect meat quality.
Thus, this study assessed the effects of including levels of crude glycerin in the diet of Boer crossbred goat kids on the qualitative and quantitative carcass characteristics as well as meat quality.

| Location, animals, and diets
Thirty-two male Boer crossbred goat kids with an initial average weight of 17.8 ± 2.2 kg and age ranging from 3 to 4 months were allocated in a completely randomized block design with four levels of crude glycerin (0, 50, 100, and 150 g/kg of (dry matter [DM] basis) and eight replicates (Table 1). Two weeks before starting the study, all animals were vaccinated and dewormed for ecto-and endoparasites and received sorghum silage as roughage ad libitum and increasing proportions of the experimental feeds. Afterwards, they were housed in individual pens within a covered shed with slatted, suspended floors, and equipped with drinking fountains and feeding troughs to ensure ad libitum access to water and food.
The goats were fed twice a day and in two equal portions, at 8 a.m. and at 4 p.m. The feed was individually weighed in a roughage:concentrate ratio of 60:40 and subsequently mixed to minimize selectiveness by the animals. Diets were formulated to be isonitrogenous (150 g/kg of CP) and isoenergetic (640 g/kg of TDN) and to meet the nutritional requirements for goats with an estimated potential average weight gain of 150 g/day (NRC, 2007

| Carcass and meat characteristics
The experiment lasted 3 months. All goats were fasted (drinking water was no withdrawn) for 16 h before recording the final live weight (LW).
The lambs were slaughtered at a commercial abattoir and the following data were recorded: body weight at slaughter (BWS), empty body weight (EBW), hot carcass weight (HCW), cold carcass weight (CCW), hot dressing percentage (HDP), and cold dressing percentage (CDP). The CCW and CDP were determined after 24-h cooling period (4°C for 24 h).
After weighing, the following carcass morphological measures were examined following Cézar and Souza (2007): the distance between the cervicothoracic joint and the first intercoccygeal joint (external carcass length, ECL); the distance between anterior edge of pubic bone and anterior edge of first rib at its midpoint (internal carcass length, ICL); All parameter measurements were taken using a metric measuring tape.
The left half-carcasses were cross-sectioned between the 12th and 13th thoracic vertebra, where the subcutaneous fat thickness (SFT) on the longissimus muscle was determined with a digital caliper. The conformation and SFT of the longissimus muscle were determined in a 1-5 scale according Osorio and Osorio (2005). In addition, measurements were taken of the maximum width (A) and the maximum depth (B). The rib eye area was assessed using the formula: REA Meat color was evaluated using a Minolta CR300 colorimeter (Minolta,1998) operating in the CIE (L*, a*, b*) system, in which L* represented lightness, a*, the intensity of the color red, and b*, the intensity of the color yellow (Cañeque & Sañudo, 2001;Miltenburg et al., 1992).
Cooking loss (CL) was determined in each loin sample with ap-proximately1.5 cm thickness, 3.0 cm length, and 2.5 cm width (Duckett et al., 1998). The meat texture was determined by the shear force (SF), by adopting the method described by Wheeler et al. (1995), expressed in kgf.

| Statistical analysis
Data were prepared using analysis of variance. The initial weight of goats was considered a covariate in the statistical model. The results were interpreted through decomposition of the orthogonal polynomials in linear and quadratic using the PROC MIXED function of the SAS (2003) software (version 9.1).
The homogeneity of variance between treatments was assumed, and the degrees of freedom were estimated using the Kenward-Roger method. The regression models were adjusted according to the significance of the parameters β1 and β2 by using the method of restricted maximum likelihood in PROC MIXED, and the estimation of parameters was obtained through the PROC REG function of the SAS software (version 9.1). All statistical procedures were performed using the value of 0.05 as the critical level of probability for error type I.

| Carcass characteristics
The DM intake linearly decreased (p < .05) as the crude glycerin inclusion level in the diet increased. Crude glycerin levels decreased (linear effect, p < .05) empty body weight (EBW), hot carcass weight (HCW), and cold carcass weight (CCW) ( Table 2).
The inclusion of crude glycerin did not affect (p > .05) cooling loss (CL), hot dressing percentage (HDP), and cold dressing percentage (CDP) ( Table 2). The mean CL value was 0.71%, which is lower than previously published results.
In addition, external carcass length (ECL) and internal carcass length (ICL) were also not influenced (p > .05) by crude glycerin levels in the diet (Table 3). Morphometric characteristics were also not significantly (p > .05) influenced by diets having the same nutritional composition.

| Qualitative characteristics muscle
Crude glycerin levels decreased (linear effect, p =.0302) rib eye area (REA) of the Longissimus dorsi muscle (Table 4). The SFT of the Longissimus dorsi muscle of goats was not affected (p > .05).
Glycerin levels did not affect (p > .05) the physical goat meat characteristics ( However, when the amounts of nutrients such as energy source and protein are changed, these variables can be influenced (Cartaxo et al., 2011). In their assessment of the effect of two energy levels The ECL and ICL were also not influenced by crude glycerin levels in the diet. This result is similar to that described by Gunn et al. (2010) and Barros et al. (2015), which studied the inclusion of crude glycerin levels (0, 15, 30, and 45%) in the diet of feedlot sheep.
Abbreviations: ECL, external carcass length; ICL, internal carcass length; ns, Not significant (p > .05); p-value, Significant probability at the 5% level; SD, Standard deviation; SEM, Standard error of the mean.
The decrease in the loin eye area (LEA) of the Longissimus dorsi muscle can be explained by the lower weight gains associated with increasing glycerin levels that negatively influenced the fat and muscle deposition of these animals. Fat deposition in animal carcasses is related to aspects such as breed, age, sex, and breeding system, and the increased REA is due to the greater BWS and age. As such, this objective measure enables the prediction of the amount of muscle in the carcass (Silva Sobrinho et al., 2008).
The SFT of the Longissimus dorsi muscle of goats was not influenced, which can be explained by the small amount of subcutaneous fat in goats, given that the largest fat deposition in these animals occurs in the abdominal and thoracic cavities.
According to Khliji et al. (2010), the acceptable limit for L* in lamb is 34-35, which is lower than the values found in this study. Meat color is a relevant characteristic at the time of purchase because it is the primary criterion used by consumers when selecting a product (except when undesired odors are present). Values obtained in this study are in agreement with those mentioned by Chanjula et al. (2015).
Cooling losses are related to those that occur during the meat preparation or cooking process and are associated with yield regarding the preparation for consumption; moreover, they influence the meat's juiciness. The shear force (SF) presented values between 1.97 and 3.17, which is classified as "soft" based on Cézar and Souza (2007).
Shear force is used to measure meat tenderness, and higher SF values denote lower meat tenderness. The values observed in this study were below with those mentioned by Lemes et al. (2013), which ranged from 3.0 to 4.7 kgf in Angorá, Crioulo, and Zebu goats (Anglo Nubian crossbreeds). The values found by the current study demonstrate that meats show great tenderness when not affected by crude glycerin.

| CON CLUS IONS
The crude glycerin can be included up to 50 g/kg DM in the diet of crossbred Boer goats without negatively affecting carcass characteristics and meat quality. It can be recommended as an energy source in finishing diets.

CO N FLI C T O F I NTE R E S T
The author has no conflict of interest to declare. Abbreviations: † , Linear effect; ‡ , Quadratic effect; CL, Cooking loss; L*, lightness, a*, redness, b*, yellowness; p-value, Significant probability at the 5% level; REA, Rib eye area; SEM, Standard error of the mean; SF, Shear force; SFT, Subcutaneous fat thickness.